The present invention relates to a valve mechanism in a multi-cylinder internal combusion engine. In particular, the invention relates to a valve mechanism which is capable of bringing the operation of an intake valve and an exhaust valve to a halt when partially halting cylinder operation in light and medium load conditions during engine operation.
In general, the pumping loss in an internal combustion engine increases in the compression stroke, so that the efficiency of fuel consumption becomes worse in what is called a "light load" condition in which there is an extra output, for example, when idling or when the vehicle descends a slope.
Hence, as a method to cope with this problem, multicylinder operation has been partially brought to a halt in accordance with the prior art, thereby enhancing the efficiency of fuel consumption.
As a method of partially halting cylinder operation in the multi-cylinder internal combustion engine, there has been employed a method temporarily stopping the jetting of fuel in an electronically injected engine. However, this method is not satisfactory since it is not available in an engine which is provided with a carburetor, and since the intake valve and the exhaust valve work as usual even in a cylinder for which fuel injection is stopped, so that air is introduced and discharged as the piston reciprocates.
Hence, as a method for partially bringing the cylinder operation to a halt, i.e. for disabling one or more cylinders, it has recently been attempted to stop the operation of the valve by forcibly increasing the gap between the rocker arm and the valve.
Until now, however, there has not been developed any valve mechanism capable of sufficiently favourably operating to stop the operation of the valve in accordance with this or other methods. Accordingly, the development of such a valve mechanism has been urgently required.
A pair of prior art mechanisms seeking to achieve this end are disclosed in Japanese Patant Publication No. 3843/1976 and Japanese Early Disclosure No. 115408/1978.